High-pressure discharge vessels with metal halide fill are subjected, in operation, to high pressures within the vessel. The wall thickness--entirely independently of the type of quartz glass used--always was a multiple of that required to withstand the given pressure within the vessel, in order to ensure that adequate safety factors were present. The result was that the external dimensions of the lamp were substantially higher than actually required by the operating conditions for the lamp if the discharge vessel volume is selected to be an optimum, considering the design requirements of the lamp, that is, for example the fill, the electrodes, and the like. Small external diameters, however, required for example for reasons of incorporation or association with optical apparatus such as reflectors or lenses, resulted in insufficient internal volume, or operation of the lamp with a discharge vessel volume which was less than an optimum. Devitrification could result.